1. Introduction
This invention relates to a means for wetting the surface of the eye, providing mechanical lubrication to the eye and reducing the evaporation of fluid from the surface of the eye. This invention also relates to a means for delivering a medicament to the corneal surface. More particularly, the invention relates to a composition capable of augmenting and maintaining a stable tear film over the corneal surface and/or to delivering a medicament to said surface. In a preferred embodiment of the invention, the invention relates to an ophthalmic composition for dry eye treatment.
2. Description of the Prior Art
It is known in the art that an aqueous tear film extends over the corneal surface which functions to maintain the corneal surface moist and lubricated. It is also known in the art that dehydration of moisture from the eye can result in discomfort, and compositions are available in the market intended to prevent evaporation from the tear film. These compositions are primarily aqueous film forming materials that provide a barrier layer that inhibits the evaporation of moisture.
The feeling of discomfort resulting from a dry eye condition includes ocular dryness, grittiness, burning, soreness or scratching dependent upon the subject and his condition. Proposed causes for dry eye, treatment and symptoms are all described in a compendium of papers on this subject edited by Holly, The Preocular Tear Film in Health, Disease, and Contact Lens Wear. The Dry Eye Institute, Lubock, Tex., 1986, incorporated herein by reference.
The most common treatment for dry eye involves temporary alleviation of the dry eye symptoms by topical application of a tear substitute that adds a volume of liquid to the anterior surface of the eye and related adnexa. Typical tear substitute compositions comprise water soluble, aqueous polymer compositions. Such compositions include, for example, saline solutions of polyvinyl alcohols, hydroxypropylmethyl cellulose or carboxymethyl celluloses. U.S. Pat. No. 4,421,748 teaches an artificial tear composition comprising an aqueous hypotonic solution of lecithin and a viscosity adjusting agent such as a solution soluble cellulose.
Methods used to quantify the effectiveness of tear substitutes for dry eye treatment solutions have not been standardized and many methods used in the art to quantify the results obtained with such tear substitute compositions are often inaccurate. For this reason, it is known that reported relief of dry eye symptoms using known tear substitutes varies considerably from subject to subject, and regardless of the method used to quantify relief using a tear substitute, relief often does not exceed several minutes.
The symptoms associated with dry eye are often exacerbated with subjects using contact lenses. In some cases, contact lens intolerance is caused in part or in total by the condition of dry eye and the symptoms thereof. For many subjects, contact lens intolerance is not overcome by topical application of tear substitutes. For these reasons, there is a need for improved compositions and processes for treatment of the dry eye condition.
An improved composition for dry eye treatment is disclosed and claimed in U.S. Pat. No. 4,914,088 granted Apr. 3, 1990 and incorporated herein by reference. This patent teaches the use of charged phospholipids and the treatment of dry eye symptoms which assist in replicating the tear film that would naturally occur in the eye. In accordance with the patent, the phospholipid composition, preferably in the form of an aqueous emulsion, is topically applied to the eye where it is believed to disperse over the ocular surface and form a film over the eye that replicates a lipid layer that would be formed by the spreading of a naturally occurring lipid secreted from the Meibomian glands over the surface of the eye during blinking. Because the phospholipid, when applied to the eye, carries a net charge, it is believed that the aligned molecules repel each other such that complex aggregate formation is prevented and the integrity of the phospholipid film is maintained. It is speculated in the patent that the film formed from the phospholipid helps in the formation of a barrier film reducing evaporation of the aqueous layer, thereby preserving the tear film.